Insulating compound.



"UNITED STATES PATENT OFFICE.

LAWRENCE E. BARRINGER AND FRANK C. ZAPF, OF SCHENECTADY, NEW YORK, ASSIGNORS T0 GENERAL ELECTRIC COMPANY, A CORPORATION OF NEW YORK.

No Drawing.

Specification of Letters Patent.

INSULATING COMPOUND.

Application filed September 12, 1911. Serial No. 648,998.

To ail whom it may concern:

Be it known that we, LAWRENCE E. BAR- mxonn and FRANK C. ZAPF, citizens of the United States, residing at Schenectady, county of Schenectady, State of New York, haveinvented certain new and useful Improvements in Insulating Compounds, of which the following is a specification.

This invention relates to insulating materials for electrical purposes and has for its object the provision of a material pf this character having a high insulating value which does notdiminish with a rise of temperature and which deteriorates very slowly with age, I

More specifically, our invention relates, to insulating materials in the nature of varnishes intended to be applied in a liquid form to a body to be insulated.

One of the uses to which insulating varnishes have been commonly put is for the purpose of making an insulating covering composed of a plurality of layers or coats of the varnish successively applied and permitted to harden before the next succeeding coat is applied. Fabrics thus treated are commonly used in the electrical arts as insulating coverings for coils and the like. Insulation of this character is disclosed in Emmet Patents 066,003 and 666,004. The particular varnish referred to in said patents, which has been commonly used for several years. is a varnish having a large percentage of an oxidizing oil, and about 80 parts to parts of rosin. Linseed oil has been most commonly employed as the oxidizing oil. We have found that China wood oil has distinct advantages over linseed 011 for this purpose and that when this is used 40 the percentage of the oxidizing oil may be reduced with advantage.

One of the most remarkable properties of China wood 'oil is its resistance to aging. It is a well known fact that when linseed oil varnishes are exposed to heat for any great length of time, the film becomes brittle. China wood oil is not thus afiected and in fact may be exposed to a temperature of 100 ,C. for a long time, after which the film is elastic and tough. This exposure to a temperature of 100 C. has been carried on for two hundred hours without affecting the film, while the same test with linseed oil varnish causes the film to become brittle and weak. With China wood oil it is unnecessary to use any of the drying agents used in linseed oil varnishes. It is the pres ence of these driers which tends to make them short-lived, aside from the oxidizing of the linseed oil itself. In China wood oil, since no driers are used, there are no harmful influences exerted from this source, and it has also been noticed that China Wood 'o-il apparently completely oxidizes less rapidly under oil. I

Instead of using China wood oil alone, we have found that a very good insulating varnish is produced by the addition of a the same conditions than linseed certain amount of rubbery pitch, such ascotton stearin pitch, which gives a great amount of elasticity to the varnish. We find, however, that the pitch has a tendency to remain permanently viscous, giving a varnish which remains somewhat tacky or sticky, and to overcome this objection, as well as to increase the disruptive strength, we add a certain amount of asphalt. The asphalt and pitch together impart to the varnish a very high insulating resistance, very much higher than where oi-l alone is used or where the base consists of a gum such as rosin or copal. The China wood oil gives the varnish a greater amount of flexibility, toughness and alonger life than can be secured with linseed oil. In some cases, as for instance where the varnish is to be used for coating cloth, paper and the like, a certain amount of a mineral oil, such as cylinder oil, may be used. This causes the varnish to flow more easily and also increases the life and elasticity of the varnish. The addition of oil of this character has also the advantage of making the varnish self healing.

In the specific embodiment of our invention, therefore, we first make a base by melting together the pitch andasphalt. After these become thoroughly mixed China wood oil is added and, if desired, cylinder oil.

The pitch which we have found very suit,

able for our purpose is a rubbery cotton stearln pitch, although other pitches of this character may be used. We have also foundthat, a certain asphalt, known as gilsonite,

serves our purpose very well, although any good hard asphalt may be used. While these materials may be combined in various proportions to produce insulating varnish, we have found the following proportions to give excellent results: 25 per cent. China wood oil, 15 per cent. cylinder oil, 30 per cent. pitch, 30 per cent. asphalt. In some cases where it is desired to quicken the drying operation so as to obtain a harder film in .a shorter time, we add a certain amount'of boiled linseed oil, In this case, of course, the proportions may also be greatly varied but the following composition has been found to work out extremely Well in practice: 27 per cent. pitch, 28 per cent. asphalt, 15 per cent. Chinawood oil, 10 per cent. cylinder oil and 15 per cent. boiled linseed oil. This constitutes a base which may be thinned for application to cloth by a solvent such as naphtha, benzol, turpentine or the like. The solvent is driven oil by baking in a well known manner after the varnish has been applied.

\Vhile We have described ourinvention as embodied in concrete form for purposes of illustration in accordance With the patent statutes, it should be understood that We do not limit our invention thereto, since various modifications thereof will suggest themselves to those skilled in theart Without departing from the spirit of our invention, the scope of which is set forth in the annexed claims.

WVhat we claim as new and desire to secure by Letters Patent of the United States, is,

1. A flexible insulating composition comprising China Wood oil, pitch and asphalt.

2. A flexible insulating compound con prising (.hina Wood oil, pitch, asphalt and a mineral oil.

3. A flexible insulating compound coinprising China wood oil, stearin pitch and asphalt.

4. A flexible insulating compound comprising China wood oil, stearin pitch, asphalt and a mineral oil.

5. An insulating compound comprising substantially twenty-five per cent. China wood oil, fifteen per cent. mineral oil, thirty per cent. pitch and thirty per cent. asphalt.

6. A tough, flexible, insulating composition consisting of a mixture of China wood oil, mineral oil, cotton stearin pitch and asphalt.

In witness whereof, we have hereunto set our hands this 11th day of September, 1911.

LAWRENCE E. BARRINGER. FRANK C. ZAPF.

Witnesses BENJAMIN B. HULL, HELEN ORFORD. 

